1. Field of the Invention
Systems consistent with the present invention relate to a broadcast receiving antenna system mounted in a wireless terminal. More particularly, the present invention relates to a broadcast receiving antenna system mounted in a wireless terminal, capable of providing optimum services and shortening the antenna length by adjusting the length of the radiating part according to magnitude of electromagnetic waves.
2. Description of the Related Art
With the recent advance of mobile communication technology, mobile terminals are providing various services that have until now been available only in limited places such as the home or office.
Among the various services, digital multimedia broadcasting (DMB) services are a new concept of mobile multimedia broadcasting service with a convergence of communication and broadcasting. DMB services are provided through wireless mobile terminals such as dedicated DMB terminals, notebook computers, mobile phone terminals, vehicle mounted terminals, personal digital assistants (PDAs), and portable multimedia players (PMPs). DMB services can be divided into satellite DMB services and terrestrial DMB services.
Terrestrial DMB services use a frequency band of 176˜212 MHz, and satellite DMB services use an S-band of 2.630˜2.655 GHz, which is higher than the terrestrial DMB band.
Typically, the length of dipole antennas is λ/2, and that of monopole antennas is λ/4. Accordingly, shorter antennas are used for higher frequency bands, and longer antennas are used for lower frequency bands. Since terrestrial DMB services use the VHF band commonly used for broadcasts, in theory they need antennas that are longer than those used for satellite DMB services and similar in length to TV antennas. Hence, terrestrial DMB services require antennas longer than about 30 cm. When the antenna output is high, the antenna may be shorter.
Terrestrial DMB services have a very small output of about 1˜2 KW because they use taboo channels 8, 10 and 12. Since channel 8, which is between channel 7 and channel 9, causes radio interference to affect neighboring channels when its output is increased, it is hard to raise the output of channel 8. However, since such an antenna is mounted in a wireless terminal which features portability and mobility, it is inconvenient to use a longer antenna.
Thus, the most urgent task of antenna developers is to shorten the length of the terrestrial DMB antenna while maintaining the reception sensitivity. Up until now it has been widely believed to be almost impossible to produce terrestrial DMB antenna below 15 cm in length.
Terrestrial DMB antennas are inevitably long because they are designed to be suitable for conditions of average reception sensitivity. However, when the reception sensitivity is good, the antenna does not need to be long. Conventional antennas are inevitably quite long because the length of the antenna is fixed.
Meanwhile, digital video broadcasting-terrestrial (DVB-T) is a digital TV broadcasting standard, which has been developed and used mostly in Europe. Digital video broadcasting-handhelds (DVB-H) are DVBs based on the DVB-T, taking into account the low power, mobility, and portability of mobile phones or portable video devices. It can be said that the DVB-H is almost equivalent to terrestrial DMB. As the DVB-H utilizes a relatively low frequency band, it generally suffers the same problems as the terrestrial DMB antenna.
Therefore, it is necessary to shorten the length of the antenna and mount the antenna in the device by adjusting the length of the antenna for receiving terrestrial DMB or the DVB-H.